navsat_transform missing child_frame_id?

edit

I am integrating GPS with odometry and IMU data. I am using two instances of robot_localization, one for the continuous data. That one feeds into a second one that gets gps data input. I use navsat_transform to transform the gps data to the proper frame. However, I found that the odometry output from navsat_transform.cpp is missing the child_frame_id. The string for that value is correctly passed to baseLinkFrameId_ but is not used in the prepareGpsOdometry method.

The result is that robot_localization does not update when passed the odometry output from navsat_transform. I was confused when I could not get output from robot_localization using the odometry from navsat_transform, yet could get output using other odometry sources as test inputs. When I saw that the child frame was missing from the navsat_transform odometry, I modified the source to supply that value and then robot_localization started responding. I don't know if that was the correct thing to do. In fact, I suppose it was not, since nobody else is having this problem, it must mean I am doing something incorrectly, but I cannot figure out what that could be.

Changing this section in navsat_transform.cpp:

  gpsOdom.header.frame_id = worldFrameId_;
  gpsOdom.header.stamp = gpsUpdateTime_;

to the following:

  gpsOdom.header.frame_id = worldFrameId_;
  gpsOdom.child_frame_id = baseLinkFrameId_;
  gpsOdom.header.stamp = gpsUpdateTime_;

fixes the problem. However, since the code is working for everyone else, I assume I am doing something wrong. Here is the navsat_transform.launch file:

<launch>

<node pkg="robot_localization" type="navsat_transform_node" name="navsat_transform_node" output= "screen" respawn="true">

  <param name="magnetic_declination_radians" value="0"/>

  <param name="yaw_offset" value="0"/>
  <param name="use_odometry_yaw" value="true" />   <!-- when true, we use yaw from the UKF, when false we use imu_data -->   
  <param name="wait_for_datum" value="false" />     <!-- when true, we use the datum parameter for initial location, when false we get it from the UKF -->

  <remap from="/imu/data" to="/imu_center" />
  <remap from="/gps/fix" to="/fix" />
  <remap from="/odometry/filtered" to="/odom_ukf" />
  <remap from="/odometry/gps" to="/odom_navsat" /> 

</node>

</launch>